We are not needed on the boss because TR have better mechanics to do this. If we could revert this situation with a stronger single target mark i bet we will be the one tanking them.
I like the concept of permamark, because i see GF mainly as a boss/elite tanking class. Yeah, we have Rush and Enforced Threat, but these are only two power in our entire list, and one of them is a paragon power.
Imo, unstoppable + sprint > block + mark. Specially if you need to get out of multiple red zones stacked in the same place. Guard is obliterated while if you sprint/dodge nothing really happens.
CW get more dps, TR get more utility, DC get more buffs e GWF get more regens, knockdowns, mobility and marks groups. GF get nothing really relevant because Iron vanguard is a better dps paragon path than Swordmaster. So, when will GF get their real tab skill?